1. Hominin to Human

2. Derived Adaptive Changes
Adaptive Radiation: Traits emerge which increase fitness
and increase variation between reproductively isolated populations

3. CHRONOLOGY OF HOMININ EVOLUTION
Term hominin used to designate human line after its split from ancestral chimps
Hominid: the taxonomic family that includes humans and the African apes and their immediate ancestors

4. CHRONOLOGY OF HOMININ EVOLUTION
If we compare Earth’s history to a 24-hour day (one second = 50,000 years):
Earliest fossils were deposited at 5:45 a.m.
First vertebrates appeared at 9:02 p.m.
Earliest mammals showed up at 10:45 p.m.
Earliest primates came at 11:43 p.m.
Earliest hominins arrived at 11:57 p.m.
Homo sapiens arrived at 36 seconds before midnight (Wolpoff, 1999)

5. Early Hominins: Common Hominid Ancestor, 8 mya
Sahelanthropus tchadensis
Orrorin tugensis
6 ꟷ 4.4 mya
Ardipithicus kadabba
Ardipithicus ramidus
4.2 ꟷ 2.0 mya
Australopithicines, Robust and Gracile
2.4 mya
Homo habilis/rudolfensis

6. Australopithecus to Homo erectus
All: bipedal, prehensile hands (Precision grip)
A. garhi may have used tools, butchered carcasses
H. habilis used tools, larger cranial vault
H. erectus produced biface hand axes, used fire, out-migrated

7. Figure 8. 2: Comparison of Dentition in Ape, Human, and A
Figure 8.2: Comparison of Dentition in Ape, Human, and A. afarensis Palates 7

8. Figure 8.3: Comparison of Homo sapiens and Pan troglodytes (the Common Chimp)

9. Figure 8.4: A Comparison of Human and Chimpanzee Pelvises9

10. Figure 8.5: A Comparison of the Skull and Dentition (Upper Jaw) of Homo and the Chimpanzee10

11. GRACILE AND ROBUST AUSTRALOPITHECINES
Two groups of South African australopithecines (3–1 m.y.a.)
Gracile (A. africanus): smaller and lighter; A. robustus: larger than gracile
Both probably descend from A. afarensis
Others contend that graciles and robusts separate species that overlapped

12. GRACILE AND ROBUST AUSTRALOPITHECINES
Front teeth are less marked than Homo
Reduced size of canines is evident
In robust australopithecines, chewing muscles are strong enough to produce a sagittal crest
Brain size increased slightly from A. afarensis (430 cm3) to A. Africanus (490 cm3) to A. robustus (540 cm3)

13. GRACILE AND ROBUST AUSTRALOPITHECINES
The 1985 discovery of “black skull” (2.6 m.y.a.) apparently an early A. robustus
Walker and Leakey view skull as an early hyperrobust A. boisei
Shows that some anatomical features did not change much during more than 1 million years

14. Figure 8.6: Skulls of Robust (left) and Gracile (Right) Australopithecines, Showing Chewing Muscles14

15. THE AUSTRALOPITHECINES AND EARLY HOMO
Homo ancestors reproductively isolated from later australopithecines by 2 m.y.a.
Hunted and gathered, made sophisticated tools, and eventually displaced its sole surviving cousin species, A. boisei
Johanson and White propose that A. afarensis split into two populations
Eventually gave rise to Homo habilis

16. OLDOWAN TOOLS Oldest tools from Olduvai Gorge are about 1.8 m.y.a.
Stone tools consist of cores and flakes
Core: piece of rock from which flakes are removed
Chopper: tool made by flaking the edge of such a core on one side

17. OLDOWAN TOOLS
Oldowan pebble tools represent world’s oldest formally recognized stone tools
Most tools at Olduvai Gorge were made from basalt

18. A. GARHI AND EARLY STONE TOOLS
In 1999, new hominin species, A. garhi, found in Ethiopia, associated with stone tools, remains of butchered animals
New species to human family tree
Demonstrated thigh bone elongated 1 million years before forearm shortened to create current human proportions
Australopithecines were tool-makers with some capacity for culture

19. EARLY HOMININS
What key traits make us human, and when and how are they revealed in the fossil record?
Who were the australopithecines, and what role did they play in human evolution?
When and where did hominins first make tools?

20. WHAT MAKES US HUMAN?
What determines whether a fossil is a human ancestor?
Look for similarities in DNA
Such key attributes as bipedal locomotion, a long period of childhood dependency, big brains, and use of tools and language
Some physical markers identify certain fossils as early hominins lost during subsequent human evolution

21. BIPEDALISM
Ardipithecus (5.8–4.4 m.y.a.): earliest recognized hominin genus; shows capacity for upright bipedal locomotion
Reliance on bipedalism differentiates the early hominins from apes
Adaptation to open grassland
More adaptive in subsequent savanna habitat
Ability to see over long grass, carry items back to a home base, and reduce body’s exposure to solar radiation

22. BRAINS, SKULLS, AND CHILDHOOD DEPENDENCY
Brain size increased during hominin evolution, especially with genus Homo
Human children have long period of childhood dependency, during which brains and skulls grow dramatically
Natural selection struck balance between structural demands of upright posture and tendency toward increased brain size

23. TOOLS Hominin stone tool manufacture dated to 2.6 m.y.a.
Upright bipedalism permitted use of tools and weapons in open grassland habitat
Primates have abilities to adapt through learning; it would be amazing if early hominins didn’t have even greater cultural abilities than contemporary apes have

24. TEETH Big back teeth: an early hominin trait
Permitted thorough chewing of tough, fibrous vegetation
Churning, rotary motion associated with such chewing favored reduction of canines and bicuspids